Methods and apparatus supporting non-persistent communications

ABSTRACT

An optical transmitter (and methods of transmitting and receiving) includes a delay and modulation circuit configured to receive at least one optical beam and a first data signal (persistent data) and generate at least two or more modulated optical beams having the first data encoded therein. One of the modulated optical beams is a time-delayed or time-shifted version of another one of the modulated optical beams, and both beams are directed toward a target. The amount or time delay between the first and second optical beams can be modulated according to a second data signal (non-persistent data) to encode the second data therein. An optical receiver is configured to detect the two modulated optical beams and recover the first data. Because changes in the amount or time delays between the first and second optical beams results in a positional change in the location of the combined centroid of the received beams at a detector of the receiver, the second data can be recovered by detecting the positional changes.

TECHNICAL FIELD

This disclosure is generally directed to laser communication systems.More specifically, this disclosure is directed to transmission ofnon-persistent or secondary communications using an optical transmitterhaving multiple lasers and reception by a resonator-based receiver.

BACKGROUND

Light waves may be made to carry information by modulating a lightsource, such as a laser source, to change one or more of the variousproperties of the light, such as amplitude, phase, frequency, orwavelength. These light waves may be in the visible spectral band, theinfrared spectral band, or another region of the electromagneticspectrum. An optical receiver receives the light waves and measures oneor more properties or variations of the light waves, such as amplitude,phase transitions, and the like, from which the information may berecovered.

Conventional optical receivers for line-of-sight communications usingmodulated light waves (such as modulated laser beams) are configured tocollect signals from a large area so that the acquired signal powerallows for accurate detection. Various optics enable the capture andfocus of light waves to concentrate the signal power at a detector inthe receiver. For some modulation schemes, such as phase modulation,conventional receivers require coherent light, so a laser is often usedas the light source. When such light is collected and focused, the bestreception occurs if all the light rays (across the cross-section of atelescope) arrive at the detector in unison as a single wavefront,maintaining alignment of the original phase relationships of the lightrays. When light rays have propagated through different media along theway or are skewed, delayed, aberrated, or otherwise affected as istypical for light waves traveling some distance through the atmosphere,free space, or any other media, the light rays tend to erode andultimately destroy the coherency of the optical signal. Without someform of wavefront correction in such systems, it is difficult orimpossible for conventional receivers to accurately demodulate anincoming optical signal.

SUMMARY

This disclosure is directed to an optical/laser communication system fortransmission (and reception) of non-persistent or secondarycommunications using an optical transmitter having multiple lasers, eachof which transmits the same persistent or primary communications datasignal to the same target.

In a first embodiment, an optical transmitter includes an optical lasersource configured to output at least one optical beam and a delay andmodulation circuit. The delay and modulation circuit is configured toreceive first data, receive second data, receive the at least oneoptical beam and transmit, using the at least one optical beam, a firstmodulated optical beam encoded with the first data in accordance with apredetermined modulation scheme. The circuit is also configured totransmit, using the at least one optical beam, a second modulatedoptical beam encoded with the first data in accordance with thepredetermined modulation scheme. The second modulated optical beam is atime-delayed version of the first modulated optical beam, and the seconddata is encoded by modulating time delays between the first and secondmodulated optical beams.

In a second embodiment, a method of transmitting optical signalsincludes receiving first data; receiving second data; receiving at leastone optical beam; and transmitting, using the at least one receivedoptical beam, a first modulated optical beam encoded with the first datain accordance with a predetermined modulation scheme. The method alsoincludes transmitting, using the at least one received optical beam, asecond modulated optical beam encoded with the first data in accordancewith the predetermined modulation scheme, wherein the second modulatedoptical beam is a time-delayed version of the first modulated opticalbeam. wherein the second modulated optical beam is a time-delayedversion of the first modulated optical beam, and the second data isencoded by modulating time delays between the first and second modulatedoptical beams.

In a third embodiment, there is provided an optical receiver includingan optical resonator and a position sensitive detector. The opticalresonator is configured to receive a first modulated optical beamcarrying first data and comprising predetermined modulation, and receivea second modulated optical beam carrying the first data and comprisingthe predetermined modulation, wherein the received second modulatedoptical beam is a time-delayed version of the received first modulatedoptical beam. The optical resonator also converts the received firstmodulated optical beam into a first intensity-modulated (IM) beam andconverts the received second modulated optical beam into a second IMbeam. The position sensitive detector is configured to detect positionalchanges of a combined centroid of the first IM beam and the second IMbeam, the detected positional changes indicative of second data.

In yet another embodiment, there is provided a method of receivingoptical signals including receiving, at a resonator-based opticalreceiver, a first modulated optical beam carrying first data andcomprising predetermined modulation, and a second modulated optical beamcarrying the first data and comprising the predetermined modulation,wherein the received second modulated optical beam is a time-delayedversion of the received first modulated optical beam. The method furtherincludes converting the received first modulated optical beam into afirst intensity-modulated (IM) beam and converting the received secondmodulated optical beam into a second IM beam. A detector receives thefirst IM beam and the second IM beam and detects positional changes of acombined centroid of the first IM beam and the second IM beam, thedetected positional changes indicative of second data.

Other technical features may be readily apparent to one skilled in theart from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following description, taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an example laser-based communication system having amulti-source (multi-laser) transmitter and a resonator-based receiver inaccordance with this disclosure;

FIG. 2A illustrates one embodiment of the transmitter shown in FIG. 1 inaccordance with this disclosure;

FIG. 2B illustrates another embodiment of the transmitter shown in FIG.1 in accordance with this disclosure;

FIGS. 3A, 3B, and 3C illustrate example time delays in multiple opticalsignals emitted from the transmitter showing correspondence to phasetransitions between symbols in accordance with this disclosure;

FIGS. 4 and 5 illustrate methods of transmitting and receiving,respectively, optical signals in accordance with this disclosure;

FIGS. 6A and 6B illustrate another example laser-based communicationsystem having a multi-source (multi-laser) transmitter and aresonator-based receiver in accordance with this disclosure;

FIG. 7 is an example illustration showing three optical beams incidenton an optical position sensitive detector in accordance with thisdisclosure;

FIG. 8 illustrates another embodiment of a position sensitive detectorin accordance with this disclosure; and

FIGS. 9 and 10 illustrate methods of transmitting and receiving,respectively, optical signals within the laser-based communicationsystem shown in FIGS. 6A, 6B and in accordance with this disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 10, described below, and the various embodiments used todescribe the principles of the present invention in this patent documentare by way of illustration only and should not be construed in any wayto limit the scope of the invention. Those skilled in the art willunderstand that the principles of the present invention may beimplemented in any type of suitably arranged device or system.

For simplicity and clarity, some features and components are notexplicitly shown in every figure, including those illustrated inconnection with other figures. It will be understood that any featuresand components illustrated in the figures may be employed in any of theembodiments described. Omission of a feature or component from aparticular figure is for purposes of simplicity and clarity and is notmeant to imply that the feature or component cannot be employed in theembodiments described in connection with that figure.

For purposes of this disclosure and as will be understood by thoseskilled in the art, the terms “light,” “light signal,” and “opticalsignal” may be used interchangeably and generally refer to anelectromagnetic signal that propagates through a given medium, which maybe empty space (such as a vacuum) or an atmospheric medium (such asair). These terms are not meant to imply any particular characteristicof the light, such as frequency, wavelength, band, coherency, spectraldensity, quality factor, etc., unless it is expressly stated orcontextually clear that such a characteristic is intended.

As described above, conventional optical receivers for line-of-sightcommunications using modulated light waves are configured to collectsignals from a large area so that the acquired signal power allows foraccurate detection, and various optics enable the capture and focus oflight waves to concentrate the signal power at a detector in thereceiver. For some modulation schemes, such as phase modulation,conventional receivers require coherent light, so a laser is often usedas the light source. When such light is collected and focused, the bestreception occurs if all the light rays (across the cross-section of atelescope) arrive at the detector in unison as a single wavefront,maintaining alignment of the original phase relationships of the lightrays. However, when light rays have propagated through different mediaalong the way or are skewed, delayed, aberrated, or otherwise affectedas is typical for light waves traveling some distance through theatmosphere, free space, or any other media, the light rays tend to erodeand ultimately destroy the coherency of the optical signal. Without someform of wavefront correction in such systems, it is difficult orimpossible for conventional receivers to accurately demodulate anincoming optical signal.

Thus, while it is generally desirable to maintain or recover thecoherency of a received optical signal or compensate for a lack ofcoherency, this is often difficult to achieve. Some prior approaches useadaptive optics to compensate for wavefront variations caused by airperturbations (also known as scintillation). Adaptive optics performwavefront correction directly on light rays and physically correctvariations. However, these approaches often have size and weightdisadvantages. Also, precise alignment of all elements of an adaptiveoptics system and precise control of the adaptive optics are generallyrequired for acceptable operation and can be difficult to achieve.

This disclosure provides systems and methods for generation andreception of modulated, such as phase-encoded or phase modulated,optical signals without the need for a locally coherent clock source(meaning no local laser or oscillator is needed at a receiver). In someembodiments, an optical resonator, etalon (such as a Fabry-Perotfilter/resonator) or other functionally equivalent structure or device,is used to convert a phase modulated optical signal into anintensity-encoded optical signal. The intensity-encoded optical signalmay be used to detect information encoded in the phase modulated opticalsignal. Various benefits can be achieved, at least in part, using anoptical front-end that includes an optical resonator configured todetect modulation transitions, such as phase variations, in a receivedoptical signal without a coherent reference source. The opticalresonator further transforms the modulation, such as the phasemodulation, into an intensity modulation that allows simplifiedprocessing, such as in the electrical domain.

Examples of various systems for which demodulation of modulated opticalsignals, such as phase-modulated optical signals, may be useful orbeneficial can include communication systems, target designators, laserguidance systems, laser sight, laser scanners, three-dimensional (3D)scanners, homing beacons, and surveying systems. In at least some ofthese examples, an optical signal is emitted and travels via a freespace signal path (known as free space optical or “FSO”) to an opticalreceiver. Although typically for use in free space propagation, thefeatures and components described here may be utilized in otherembodiments, such as those employing a fiber coupling or anotherwaveguide system. Systems and method for demodulation of phase-modulatedoptical signals in accordance with aspects and examples disclosed heremay be applied to any of the above example optical systems or othersystems to generate, transmit, receive, detect, and recover usefulinformation from an optical signal having phase encoding.

Those of ordinary skill in the art will understand that optical signalsmodulated to carry information have one or more characteristics that arechanged by a transmitter in either a continuous or discrete fashion orsome combination of the two, and segments of the light over time may beassociated with the particular characteristic(s) that indicate theinformation being conveyed. For example, a phase modulated digitaloptical transmitter may emit coherent light of a certain phaserelationship (relative to a reference time and/or phase) to indicate aparticular value. The light emitted to indicate the value may beconsidered a segment or length of light whose phase indicates the value.Later, the transmitter will alter the light characteristic to emit asecond segment of light to indicate a second value, then a third segmentof light, then a fourth segment of light, and so on. As will beappreciated, a “symbol” is transmitted within each segment, and thesegment length is often referred to as the symbol length. The rate atwhich the transmitter discretely alters the characteristic, as in thisexample, is a modulation rate of the transmitter, also known as a symbolrate. Each segment of light has an associated physical length that isbased upon the duration and the speed of light in the propagationmedium. For example, a modulation rate of 10⁸ symbols per second (100million transitions per second) emits light segments of 10 nanosecondduration with a length of approximately 3 meters. Higher modulationrates generate shorter light segments, and lower modulation ratesgenerate longer light segments. Various embodiments of this disclosuremay operate at even higher transmission rates, such as 1 trilliontransitions per second (1 Giga symbol/sec) or more. It will beunderstood that a single light segment may have one of multiple phasevalues (and possibly amplitude values), and therefore the indicatedvalue may be a multi-bit binary value (symbol). Accordingly, modulationrate is not necessarily equal to a transmission bit rate for atransmission system.

In addition to phase modulation of the emitted light, some opticaltransmission systems may alter different or additional lightcharacteristics, such as amplitude, intensity, frequency, or wavelength,and may also vary the modulation rate over time, such as based onchannel characteristics, noise, error rate, and the like. Additionally,some optical transmission systems may modulate light in an analogfashion, such as by a continuous variation in amplitude of the lightsignal, and therefore not employ a modulation rate per se. For purposesof this disclosure, aspects and embodiments are generally described inthe context of a discrete transmission system including phasemodulation, although it will be understood that aspects and embodimentsdisclosed here may be equally useful as transmitters and receivers fortransmission systems that generate light signals conveying informationdifferently than that described (such as a combination of phase andamplitude modulations).

In addition, it will be understood that examples of methods andapparatuses discussed herein are not limited in application to thedetails of construction and the arrangement of components set forth inthe following description or illustrated in the accompanying drawings.The methods and apparatuses are capable of implementation in otherexamples and of being practiced or carried out in various ways. Examplesof specific implementations are provided here for illustrative purposesonly and are not intended to be limiting. Also, the phraseology andterminology used here are for purposes of description and should not beregarded as limiting. Thus, for example, any references to front andback, left and right, top and bottom, upper and lower, or vertical andhorizontal are intended for convenience of description, not to limit thepresent systems and methods or their components to any one positional orspatial orientation.

FIG. 1 illustrates an example laser-based communication system 10including a laser optical transmitter 100 and a resonator-based receiver150 in accordance with this disclosure. Note that while the componentsof the optical transmitter 100 and the optical receiver 150 identifiedin FIG. 1 (and other Figures) may be shown and described as discreteelements in a block diagram and may be referred to as “module,”“circuitry,” or “circuit,” these components may be implemented in anysuitable manner. For example, these components may be implemented as oneor a combination of analog circuitry, digital circuitry, or one or moreprocessing devices executing software instructions. In some embodiments,components may be implemented using one or more microprocessors,microcontrollers, digital signal processors (DSPs), application-specificintegrated circuits (ASICs), or field programmable gate arrays (FPGAs).Unless otherwise indicated, signal lines between components of theoptical transmitter 100 and between components of the optical receiver150 may be implemented as discrete analog, digital, or optical signallines. Some of the processing operations may be expressed in terms ofcalculations or determinations performed by the optical transmitter 100,the optical receiver 150, a detector, a controller, or other components.The equivalent of calculating and determining values or other elementscan be performed by any suitable analog or digital signal processingtechniques and are included within the scope of this disclosure. Unlessotherwise indicated, signals may be encoded in either digital or analogform.

In the illustrated embodiment, the optical transmitter 100 includes adelay and modulation circuit 125 a configured to receive one or moreoptical beams from a laser source 116 and an input/data signal 110, suchas a digital bit stream. As will be appreciated, the delay andmodulation circuit 125 a receives the input information and controlsmodulation of the one or more optical beams to generate and output aplurality of modulated or encoded optical beams 120 a-120 n eachcarrying the same input information. Each of the beams 120 a-120 n aremodulated in the same manner and carry the same data. However, at leastone of the modulated optical beams 120 a-120 n is time shifted, ordelayed in time (time-delayed) with respect to another one of themodulated optical beams. In other words, the timing or time position ofthe data (or symbols) carried on one respective optical beam is shiftedrelative the data (or symbols) carried on another respective opticalbeam. This results in a time difference (or phase delay) between whenthe symbol transitions occur in one respective optical beam and when thesame symbol transitions occur in the other respective optical beam.

The one or more optical beams are controlled or modulated in accordancewith a desired encoding protocol established for transmission of theinformation. In other words, one or more control signal(s) are generatedthat, when applied to a modulator, modulate or modify properties of theoptical beam(s) in order to carry the information. It will be understoodthat the input/data signal 110 including the data may be in analog ordigital form. In addition, in one embodiment, the optical beams 120a-120 n each have essentially the same wavelength of light, while inanother embodiment, the optical beams 120 a-120 n have similarwavelengths. Similar wavelengths are wavelengths that satisfy theequation

$\frac{{Ni}\;\lambda_{i}}{2} = {{nL} + {\Delta\; L_{i}}}$where N is an integer number, nL is the optical length of the etalon (atthe receiver), λ_(i) is the wavelength of the beam “i”, and values of|ΔL_(i)|/λ_(i) are within 5% of each other, and in some embodimentswithin 1% or 2% from each other.

As will be described in further detail below and in other figures,generating the modulated optical beams 120 a-120 n having delay(s) withrespect to each other may be implemented or accomplished in differentways. In various embodiments, one or more delay(s) may be added inelectrical signal path(s), one or more delays may be added in opticalpath(s), or in a combination thereof.

One example of adding delay(s) in the electrical path may includeduplicating or splitting the input signal 110 (or signal(s) generatedafter encoding) into a plurality of such signals, adding delay(s) to oneor more of the signals to produce a plurality of time-shifted signals,and applying each signal to corresponding modulators that generate thecorresponding modulated optical beams 120 a-120 n.

One example of adding delay(s) in the optical path may include applyingthe input signal 110 (or signal generated after encoding) to a modulatorto generate one modulated optical beam which is then split or duplicatedand an optical delay may be inserted into one or more of the splitoptical beams to output the corresponding modulated optical beams 120a-120 n. Another example of adding delay(s) in the optical path mayinclude applying the input signal 110 (or signal generated afterencoding) to a plurality of modulators (each receiving a separateoptical beam) that generate a plurality of modulated optical beams(identical with respect to the timing of the data being carried), andthen an optical delay may be inserted into one or more of the modulatedoptical beams to output the corresponding modulated optical beams 120a-120 n. As will be appreciated, numerous configurations andarrangements may be utilized as desired to generate the modulatedoptical beams 120 a-120 n with at least one being time-delayed withrespect to another.

In the illustrated embodiment in FIG. 1, the optical receiver 150includes an optical resonator 160, one or more optics 170, and adetector 180.

As will be appreciated, the optical receiver 150 is referred to as a“resonator-based” receiver. An “resonator-based” receiver includes aresonator or an “etalon” which includes various devices and structures.Note that the use of the term “resonator” throughout this disclosure isnot intended to be limiting and as used here may include any of multiplestructures, such as plates with reflecting surfaces and parallel mirrorswith various materials (which may or may not include active opticalmaterials) positioned in-between. The spacing between the firstsemi-reflective surface and the second semi-reflective surface of anetalon may be referred to as a “cavity” but is not so limited. Opticalresonators may include other suitable structures, such asinterferometers and the like. Additionally, resonator (and etalon)structures may be formed as a laminate, layer, film, coating, or thelike. This may include Fabry-Perot etalons, micro-rings, optical delayline(s), optical resonators or other types of resonators (including butnot limited to common-path or double-path interferometers), which areconfigured to sense variations, such as phase variations or modulations,in the received optical signals 120 a-120 n. Accordingly, all of theforegoing structures and devices will be commonly referred to as a“resonator” or “optical resonator” herein. In one specific embodiment,the resonator 160 is an etalon.

The optical resonator 160 may include one or multiple resonators oretalons. In other embodiments, for example, each of the receivedmodulated optical signals 120 has a corresponding resonator 160. Ifseparate resonators 160 are used for different signals, different optics170 may be used with the different resonators 160, and differentdetectors 180 may be used with the different resonators 160 and thedifferent optics 170.

In some embodiments, the resonator 160 may be coupled to a pump source(such as a laser), which may excite one or more components (such as anactive optical medium) of the resonator 160 to generate an optical gainin the received optical signals 120 a-120 n. The variations in each ofthe received optical signals 120 a-120 n are representative of themodulation performed at the optical transmitter 100. That is, thevariations may be representative of information encoded at the opticaltransmitter 100. The resonator 160 transforms the variations into anintensity modulation of output optical signal energy, which are shown asoutput optical signal energy 165 a-165 n in FIG. 1B. More specifically,the resonator 160 converts a phase modulation of each received opticalsignal 120 a-120 n in part by interaction of the arriving optical signal120 a-120 n with resonant optical signal energy accumulated within theresonator 160.

In some embodiments, the resonator 160 (or multiple resonators) mayinclude a pair of parallel semi-reflective surfaces with an at leastsemi-transparent medium interposed therebetween. The semi-transparentmedium may represent an active optical medium that provides an opticalgain (such as an amplitude increase) when excited by an optical orelectrical signal. For additional examples of optical resonators andetalons (and details thereof), reference can be made to U.S. Pat. No.10,313,022, which has been incorporated by reference.

The resonator 160 may have one or more characteristic resonantfrequencies, each associated with a certain wavelength of light, basedupon the spacing (the optical length) between the semi-reflectivesurfaces. In some embodiments, the surfaces are semi-reflective andsemi-transmissive, allowing some light through. Accordingly, thearriving optical signals 120 a-120 n may be allowed into the resonator160 (between the pair of semi-reflective surfaces) and may resonateinside the resonator 160 and between the pair of semi-reflectivesurfaces. In addition, some of the resonating optical signal energyinside the resonator 160 is emitted from the resonator 160 through oneof the semi-transmissive surfaces (referred to as the “output opticalsignal energy”). The output optical signal energy emitted from theresonator 160 is shown here as the optical signal energy 165 a-165 n inFIG. 1.

The optical signals 120 a-120 n received at the resonator 160 mayestablish a steady-state energy-preserving condition in which eachoptical signal 120 a-120 n continuously arrives at the resonator 160,accumulates or adds to build-up resonating optical signal energy insidethe resonator 160, and emerges from the resonator 160 at a constant rate(meaning a steady-state output value). A variation in the arriving phaseand/or frequency of each of the optical signals 120 a-120 n will disruptthe optical signal energy resonating inside the resonator 160 and,accordingly, disturb the corresponding output optical signal energy 165a-165 n. Variations in the arriving amplitude/intensity of each opticalsignal may also disrupt energy resonating and cause a similardisturbance. Once the steady-state condition is re-established (meaningeach respective optical signal 120 a-120 n arrives at a constant ratewithout a variation), the respective output optical signal energy 165a-165 n returns to the corresponding constant rate.

Accordingly, a change in phase, frequency, or amplitude (or intensity)of the arriving optical signals 120 a-120 n causes a change in intensityof the emerging output optical signal energy 165 a-165 n. A large phasetransition in the arriving optical signals 120 a-120 n, for example,causes a large (but temporary) intensity change in the emerging outputoptical signal energy 165 a-165 n. Similar operation occurs in amicro-ring or other optical resonator. Accordingly, in various examples,the resonator 160 functions as a demodulator or a modulation converterfor one or more received optical signals 120 a-120 n. Each of theemerging output optical signal energy 165 a-165 n therefore carries thesame informational content as the arriving optical signals 120 a-120 n,but in intensity-modulated form.

The output optical signal energy 165 a-165 n is directed to the detector180 via the optics 170. The detector 180 converts the emergingintensity-modulated output optical signal energy 165 a-165 n into anelectrical signal 185. In some embodiments, the detector 180 may includeone or more photodetectors, such as one or more photodiodes. In theembodiment shown, the detector 180 functions to sum theintensity-modulated output optical signal energy 165 a-165 n and outputthe electrical signal 185 (representing the total power received at thedetector 180. The electrical signal 185 may be further processed by adigital or analog processing subsystem to recover the data payload. Oneexample of such a processing subsystem is described in U.S. Pat. No.10,313,022 and includes an analog-to-digital converter and a digitalprocessing subsystem (which may function as a correlator and a codegenerator or which may perform any other suitable processing). Referenceis also made to U.S. Pat. No. 10,305,602 (which is hereby incorporatedby reference in its entirety) for a description of a demodulator for thedemodulation of a QAM-modulated optical beam (having I and Q components)using multiple resonators/etalons and various output responses ofresonators/etalons to phase and/or amplitude transitions in the receivedoptical signal.

As will be appreciated, in another embodiment (not shown), the detector180 may generate and output multiple electrical signals that correspondto each of the optical signal energy beams 165 a-165 n received at thedetector 180. These multiple electrical signals may be further processedindividually by a digital or analog processing subsystem to recover thedata payload, or otherwise summed and then processed.

In some embodiments, the optical receiver 150 may include additional orfewer optics than discussed above and may omit or add various othercomponents relative to those discussed above. For example, the optics170 may include focusing optics configured to receive the emergingoutput optical signal energy 165 a-165 n from the resonator 160 and tofocus the output optical signal energy 165 a-165 n on the detector(s)180. Also, the optical receiver 150 may include one or more optics thatfocus or otherwise collect and direct the received optical signals 120a-120 n to the resonator 160.

In some embodiments, the resonator 160 may include reflective surfaces(including semi-reflective surfaces) that are not co-planar and/or arenot co-linear. For example, an interior reflective surface of aresonator 160 may include some curvature, and an opposing surface mayalso be curved such that a distance between the two surfaces issubstantially constant across various regions of the resonator 160. Inother embodiments, an resonator 160 may have non-linear or non-planarsurfaces with varying distances between the surfaces at various regionsand may still function as an optical resonator or etalon for variouswavelengths and at various regions suitable for use in examplesdiscussed here. Accordingly, a resonator 160 may be purposefullydesigned to conform to a surface or to have various regions responsiveto differing wavelengths or responsive to differing angles of arrivalfor a given wavelength.

In some embodiments, the resonator 160 may be coupled to a pump source,which may excite one or more components (such as an active opticalmedium) of the resonator 160 to generate an optical gain in one or morereceived optical signals. In other embodiments, the resonator 160 maynot include any pump source.

Now turning to FIG. 2A, there is shown one example (and more detailed)embodiment of the optical transmitter 100 of FIG. 1, denoted in FIG. 2Aas optical transmitter 100 a. As will be understood, the opticaltransmitter 100 a illustrates an optical transmitter in which one ormore delay(s) are incorporated or inserted into an electrical signalpath which results in the desired modulated optical beams 120 a-120 n.For ease of reference and example, this embodiment is illustrated withreference to outputting at least three modulated optical beams 120 a,120 b, 120 n. In other embodiments, the number of transmitted beams 120may be two or more.

In this embodiment, a delay and modulator circuit 125 a is shown asincluding a phase or time delay circuit 114 a having delay elements 140a-140 n and a plurality of modulators 118 a-118 n—one for each opticalbeam. Also in this specific embodiment, the laser source 116 includes aplurality of laser sources 116 a-116 n each outputting an optical beamto be modulated by the respective modulator 118 a-118 n.

In one embodiment, the raw data or input signal 110 is applied to anencoder 112 that generates one or more control signals 115 forcontrolling, at a minimum, phase modulation of the optical beam(s) bythe modulators 118 a-118 n. In other embodiments, the signal(s) 115 mayinclude multiple signals each to control a modulation of a differentproperty of the optical beams, e.g., phase, amplitude/intensity,frequency, wavelength, etc. For example, the control signal(s) 115 mayinclude two signals—one for controlling phase modulation and anothercontrolling amplitude modulation. Various combinations may be utilized.Depending on the specific protocol, this may result in modulating theoptical beam(s) to carry information in a QAM-type modulation scheme(both phase and amplitude) as ultimately applied to the optical beam. Aswill be appreciated, other types of ultimate modulation schemes may beused, such as n-QAM, phase-shift keying (xPSK), etc., and the encoder112 is not limited in generating the content and structure of thecontrol signal(s) 115 for controlling the modulators. It will beunderstood that the specific protocol(s)—or specific encoding andmodulation scheme(s))—which describe the correspondence between thetransmitted information and the changes in the optical beam propertiesare not further described, nor are any further descriptions otherwiserequired for an understanding of the concepts taught herein. As will bedescribed below, those skilled in the art will understand that benefitsof the system described herein can be achieved from detecting changes inphase (or equivalent change in frequency), and in other embodiments,changes in amplitude/intensity

The optical transmitter 100 a includes a plurality of optical sources116 a-116 n, such as different laser sources, each for generating andemitting a respective light/optical beam or wave 117 a-117 n (opticalsignals). Any number of optical sources 116 a-116 n may be utilized, asdesired, including an embodiment in which there is a laser source thatgenerates single optical beam 117 that is split and applied to each ofthe modulator(s) 118 a-118 n. Each optical source 116 a-116 n emits thelight beam 117 a-117 n that is modulated by a modulator 118 a-118 n togenerate and output the modulated optical signal or beam 120 a-120 n. Aswill be appreciated, each modulator 118 may be configured to modulateeach respective light beam 117 in one or more ways.

In some embodiments, the optical sources 116 a-116 b output light havingthe same wavelength or similar wavelengths. Each of the optical sources116 a-116 n is either aligned to or aimed at the optical receiver 150,and the optical sources 116 a-116 n are spatially disposed from eachother. The actual spacing or positioning of the optical sources 116a-116 n may vary. In one embodiment, any suitable output structure 130,such as various optic(s), that may include one or more optical lens orother optical transmission component, such as a steering mirror,transmitting telescope, beam expander, fiber line, and/or other focusingmechanism may be used to direct the modulated optical signals or beams120 a-120 n towards a target, i.e., the optical receiver 150, as needed.

Depending on the positional accuracy of the multiple lasers 116 a-116 nwith respect to each other, as well as the layout configuration ofcomponents and conductors in the transmitter, one laser's output may beeffectively time delayed or offset with respect to another laser'soutput—even with no delay intentionally added using one of the delayelements 140 a-140 n. Though largely unintentional, such delay(s) mayresult in a significant time delay between outputs thereby causingdifficulty for conventional receivers to receive/decode the receivedbeams.

In one embodiment, the modulator 118 functions to modulate the lightbeam 117 in response to the control signal(s) 115, which may include onor more of phase/frequency, amplitude, intensity and/or wavelengthmodulation (or modulation of another characteristic of the signal whichmay be known to those skilled in the art). For purposes of explanationonly, this disclosure will describe examples with reference to phasemodulation, but other or additional modulations may be applied to thesignal. It will be understood that, depending on the magnitude of thephase change, that either the term “phase modulation” or “frequencymodulation” could be used. Although in many cases, phase modulation isconsidered to be different from frequency modulation, this patentdocument defines phase modulation to include both phase and frequencychanges, unless specifically stated otherwise or is readilyascertainable from the context of use. Thus, the term “phase modulation”as utilized herein is intended to be broad and include equivalentchanges in frequency. Further, in other embodiments, one or more othertechniques known to those skilled in the art can also be applied orperformed to modulate a characteristic of the light beam 117, such asamplitude, intensity, frequency, wavelength or variation in themodulation rate over time.

The phase or time delay circuit 114 a is configured to receive thecontrol signal(s) 115 and generate one or more time-delayed controlsignal(s) 115 a-115 n—as shown. As will be appreciated, each of thesignals 115 a-115 n are duplicates or copies of the original signal(s)115, but are shifted in time with respect to each other. In other words,other than being shifted in time (a phase difference) with respect toeach other, each of the signals 115 a-115 n correspond or match, orotherwise have essentially the same waveform. Also, not each of thesignals 115 a-115 n are required to have different time shifts ordifferentials. In most embodiments, at least one should be offset intime from another one.

Each of the time-delayed control signal(s) 115 a-115 n is input to eachof the respective modulators 118 a-118 n to individually modulate therespective light beams 117 a-117 n output from the optical sources 116a-116 n. The phase or time delay circuit 114 a functions tointentionally inject a time or phase delay into one or more of thereplicated control signal(s). In some embodiments, for example, thecircuit 114 includes one or more delay elements 140 a-140 n, where eachdelay element functions to inject or generate a time delay of apredetermined specified amount (which can be fixed, programmable, orotherwise variable—as more fully explained below with respect to FIGS.6A-6B).

The delay elements 140 a-140 n include any suitable structuresconfigured to delay an electrical signal by one or more fixed orcontrollable amounts. In some embodiments, each of the delay elements140 a-140 n may represent separate components, such as when each of thedelay elements 140 a-140 n is implemented using separate inverter chainsor other sequential delay elements. In other embodiments, the delayelements 140 a-140 n may be implemented using a common structure, suchas when all of the delay elements 140 a-140 n are implemented using asingle inverter chain or other sequential delay elements (with taps atgiven locations for desired amounts of delay). Note that it may also bepossible to implement different delay amounts using different electricaltraces/conductors of different lengths. In general, this disclosure isnot limited to any particular technique or structures for delaying anelectrical signal by a fixed or controllable amount.

In FIG. 2A, the transmitter 100 a is shown having an optional controlcircuit 210 a (shown in block diagram form). Persons of ordinary skillin the art will readily understand that any suitable device(s), logic,or circuits (and methods) may be utilized, as desired, to generate andoutput delay control signals for controlling the delay elements 140a-140 n to provide delay(s) in the signal paths 115 a-115 n inaccordance with the teachings herein. As will be appreciated, thecontrol circuit 210 a may be controlled by a processor (not shown)operating in accordance with one or more software or firmware programs.The control circuit 210 a may be further configured to operate thetransmitter 100 a in one or more modes of operation, as described below.

As described above, the phase or time delay circuit 114 receives thecontrol signal(s) 115 and applies the signal(s) 115 to each of multipledelay elements 140 a-140 n, which are optionally controlled using one ormore signals 211 a from the control circuit 210 a. Collectively, thedelay elements 140 a-140 n output respective delayed control signals 115a-115 n, where each control signal 115 a-115 n has been delayed orshifted by the respective delay amount. The delayed control signals 115a-115 n are then applied to the modulators 118 a-118 n which modulatethe light beams 117 a-117 n in accordance therewith, to generate themodulated optical signals 120 a-120 n. In another embodiment, forexample, one of the control signals 115 a-115 n may represent anundelayed version of the control signal(s) 115, and no delay element maybe used to generate that version of the control signal.

As will be appreciated, FIG. 2A illustrates delaying the phasemodulation signal. However, as noted above, the signal 115 could includemultiple separate signals, with each separate signal modulating adifferent characteristic (e.g., phase, amplitude, intensity, frequency,wavelength) of the laser beam. In other embodiments, additional delayelements (or other configurations of delay elements) could be added suchthat the delay of each type of modulation can be controlled (or notcontrolled) individually.

The length of the delay(s) introduced by the circuit 114 will generallybe less than a symbol length (length of symbol encoded in the datasignal 115), but substantially larger in magnitude in terms of thewavelength(s) of the optical sources 116 a-116 n. The introduction ofdelays or time offsets in one or more of the control signals 115 a-115 neffectively renders the transmitted optical signals 120 a-120 nextremely difficult to receive and demodulate in conventional receiversthat utilize adaptive optics and fiber, making them hard-to-intercept.It has been found that when the time delays between the optical sources116 a-116 n are small relative to the length of a transmitted symbol,all symbols can be still recovered by the optical receiver 150 describedherein. In other words, the injected time delay has virtually no effecton reception and demodulation of the underlying symbols and data.Therefore, multiple-laser transmissions can be used in place ofsingle-laser transmission, provided the total power requirements are metor essentially the same.

Without the introduction of one or more delays, conventional receiversutilizing adaptive optics and fiber (now or in the future) willgenerally have the ability to receive and demodulate the optical signals120 a-120 n transmitted from the multiple optical sources 116 a-116 n.In some embodiments, the transmitter 100 a may therefore enable orsupport two different modes of receiver operation. A hard-to-interceptmode can be enabled when one or more delays are added in one or morepaths of the control signals 115 a-115 n. In this mode, the transmittedsignals 120 a-120 n are successfully received and demodulated using theoptical receiver 150 in accordance with this disclosure. A normal modecan be enabled when no delays are added. In this mode, although thetransmitted signals 120 a-120 n can still be successfully received anddemodulated using the optical receiver 150, a conventional receiverusing adaptive optics and fiber may also have the ability tosuccessfully receive and demodulate the transmitted signals 120 a-120 n.

The amount (or length) of the delay(s) may be fixed, dynamic,programmable, variable, or involve any combination(s) thereof. In otherembodiments, the amount/length of the delay(s) may vary randomly—whichwould necessarily increase the distortions and incoherency of thetransmitted light beams 120 a-120 n and render reception by aconventional receiver even more difficult. These may be random delayamount(s) in the signal path(s) and for random period(s) of time.

In one embodiment, the laser-based communication system 10 utilizesmultiple laser optical sources 116 a-116 n and simultaneously modulateseach of the multiple optical sources 116 a-116 n (with nointentionally-added delays in the encoded data signal path) in essenceaccording to the same encoded data signal 115. Prior systems thatutilize a single laser source (single channel) require all of thereceived optical power at a receiver to originate from the singlehigh-power laser source. In contrast, the multiple laser optical sources116 a-116 n in the laser-based communication system 10 enables the useof lower cost low-power lasers, where an additive effect is achieved bythe resonator 160 when receiving multiple versions of the same signal(the optical signals 120 a-120 n) from the multiple optical sources 116a-116 n and modulators 118 a-118 n.

In another embodiment, the laser-based communication system 10 utilizesmultiple laser optical sources 116 a-116 n and modulates at least one ofthe multiple optical sources 116 a-116 n with one of the control signals115 a-115 n and modulates at least another one of the multiple opticalsources 116 a-116 n with a delayed (or time offset) version of thecontrol signals 115 a-115. In other embodiments, any number ofadditional path(s) and delay(s) may be provided, and delay amount(s) forall or some of the delay elements 140 a-140 n may be different,resulting in encoded data signals in which at least one is offset intime from another one (or more). As will be described further below, theinclusion of a substantial delay in application of at least one of thecontrol signal(s) 115 a-115 n to one or more of the light beams 117a-117 n will render the transmitted beams 120 a-120 n difficult todetect/receive/recover by a conventional optical receiver—even whenadaptive optics may be utilized. Insertion of such a delay (or delays)causes substantial wavefront distortion or mismatch (or incoherency) inthe transmitted beams 120 a-120 n that renders them difficult to detect.

Although FIG. 1 illustrates one example of a laser-based communicationsystem 10 having a multi-source (multi-laser) transmitter 100 (or 100 ashown in FIG. 2A) and a resonator-based receiver 150, various changesmay be made to the system. For example, the system 10 may include anysuitable number of transmitters 100, receivers 150, and/or transceiversincorporating transmitters 100 and receivers 150.

It will be appreciated that only those components of the opticaltransmitter 100, 100 a needed to explain and understand the concepts,methods, and systems disclosed herein are shown in the FIGURES anddescribed herein. Although not shown, the optical transmitter 100, 100 amay include various other components as needed or desired. In someembodiments, the optical transmitter 100 a may be configured in the sameor similar manner as the optical transmitter described in U.S. Pat. No.10,313,022 (which is hereby incorporated by reference in its entirety)and may further include a forward error correction (FEC) module, aspreading module, a mapping module, and/or a pulse-shaping filter.Additional optics may also be included, such as one or more mirrors orlenses, which direct each of the modulated optical signals or beams 120a-120 n for output. For example, the optics can be used to direct themodulated optical signals 120 a-120 n in a direction of the opticalreceiver 150 via a signal path as shown in FIG. 1.

Note that while communication in FIG. 1 is shown as being one-way fromthe optical transmitter 100 to the optical receiver 150, end devices mayinclude both an optical transmitter 100 and an optical receiver 150(such as an optical transceiver) to support bidirectional datacommunication. Each transceiver may be capable of bidirectional datacommunication with another transmitter/receiver pair.

Now turning to FIG. 2B, there is shown another example (and moredetailed) embodiment of the optical transmitter 100 of FIG. 1, denotedin FIG. 2B as optical transmitter 100 b. As will be understood, theoptical transmitter 100 b illustrates an optical transmitter in whichone or more delay(s) are incorporated or inserted into an optical signalpath which results in the desired modulated optical beams 120 a-120 n.For ease of reference and example, this embodiment is illustrated withreference to outputting at least three modulated optical beams 120 a,120 b, 120 n. In other embodiments, the number of transmitted beams 120may be two or more.

The transmitter 100 b of FIG. 2B includes various components shown inthe transmitter 100 a of FIG. 2A and described above. As will beappreciated, the transmitter 100 b may form one component in anotherembodiment of a laser-based communication system that also includes theresonator-based receiver 150 illustrated in FIG. 1. One obviousdifference between the transmitters 100 a and 100 b is the position andconfiguration of the phase or time delay circuit 114. In transmitter 100a, the delay circuit 114 a is disposed to provide delay(s) in one ormore electrical path(s) to perform electrical path delaying, while intransmitter 100 b, a delay circuit 114 b is disposed to provide delay(s)in one or more optical path(s) (after the optical beams have beenmodulated) to perform optical path delaying.

In one embodiment, the raw data or input signal 110 is applied to theencoder 112 that generates the one or more control signals 115 forcontrolling, at a minimum, phase modulation of the optical beam(s) bythe modulators 118 a-118 n—as similarly described above with respect tooptical transmitter 100 a. Also, in the specific embodiment illustrated,the optical transmitter 100 b includes a plurality of optical sources116 a-116 n, such as different laser sources, each for generating andemitting a respective light/optical beam or wave 117 a-117 n (opticalsignals). Any number of optical sources 116 a-116 n may be utilized, asdesired, including an embodiment in which there is a laser source thatgenerates a single optical beam 117 that may be split (e.g., opticalsplitter, not shown) and applied to each of the modulator(s) 118 a-118n. In the embodiment shown, each optical source 116 a-116 n emits thelight beam 117 a-117 n that is modulated and output by the modulator 118a-118 n to generate modulated optical signals or beams.

One or more of the modulated optical signals or beams coming from themodulators 118 a-118 n are input to a delay circuit 114 b. The phase ortime delay circuit 114 b functions to intentionally inject a time orphase delay into one or more of the modulated optical beams prior totransmission to a target. In some embodiments, for example, the circuit114 b includes one or more delay elements 141 a-141 n, where each delayelement functions to inject or generate a time delay of a predeterminedspecified amount (which can be fixed, programmable, or otherwisevariable.

The delay elements 141 a-141 n (optical delay lines or elements) includeany suitable structures configured to delay an optical signal by one ormore fixed or controllable amounts. In some embodiments, each of thedelay elements 141 a-141 n may represent separate components, such aswhen each of the delay elements 141 a-141 n is implemented usingseparate chains or other sequential delay elements. In otherembodiments, the delay elements 141 a-141 n may be implemented using acommon structure, such as when all of the delay elements 141 a-141 n areimplemented using a single chain or other sequential delay elements(with taps at given locations for desired amounts of delay). Variousstructure(s) or methods are known to, and may be implemented by, thoseof skill in the art. In general, this disclosure is not limited to anyparticular technique or structures for delaying an optical signal by afixed or controllable amount.

In FIG. 2B, the transmitter 100 b is shown having an optional controlcircuit 210 b (shown in block diagram form). Persons of ordinary skillin the art will readily understand that any suitable structure(s),device(s), logic, or circuits (and methods) may be utilized, as desired,to generate and output delay control signals for controlling the delayelements 141 a-141 n to provide delay(s) in accordance with theteachings herein. As will be appreciated, the control circuit 210 b maybe controlled by a processor (not shown) operating in accordance withone or more software or firmware programs. The control circuit 210 b maybe further configured to operate the transmitter 100 b in one or moremodes of operation, as described above with respect to opticaltransmitter 100 a.

In FIG. 2B, the phase or time delay circuit 114 b receives the modulatedoptical signals output from the modulators 118 a-118 n and applies oneor more optical delays which are optionally controlled using one or moresignals 211 b from the control circuit 210 b. Collectively, the delayelements 141 a-141 n output the respective delayed modulated opticalbeams 120 a-120 n. In another embodiment, for example, one of themodulated optical beams 120 a-120 n may represent an undelayed versionand no delay element may be used to generate that version of the controlsignal.

The length of the delay(s) introduced by the circuit 114 b willgenerally be the same as the delay(s) introduced by the circuit 114 a inthe embodiment shown in FIG. 2A. As will be appreciated, the operationaldescription, various embodiments, teachings, and concepts applicable anddescribed above with respect to operation of the optical transmitter 100a above are also applicable and may be applied to the opticaltransmitter 100 b. As will be appreciated however, insertion of the timedelay(s) in this manner will cause all modulation(s) (e.g., phase,amplitude, frequency, wavelength, etc.) in the modulated output signalto be collectively delayed.

Although the embodiments of the transmitters 100 a and 100 b are shownseparately, a person of skill in the art will understand that the twoembodiments could be combined in whole or in part to generate themodulated optical beams 120 a-120 n in which at least one of the beamsis time-shifted or delayed from another one of the beams.

FIGS. 3A, 3B, and 3C illustrate example time delays in multiple opticalsignals (such as signals 120 a-120 n) emitted from the transmitter 100,100 a, 100 b that correspond to phase transitions between symbols inaccordance with this disclosure. In particular, FIGS. 3A, 3B and 3Cillustrate an example propagation of coherent light from the opticaltransmitter through a realistic medium (such as air), where the lightmay encounter aberrations (such as air perturbations). The light raysare influenced by air perturbations or other obstructive influences thatmay affect a portion of each of the signals 120 a, 120 b, 120 ndifferently than adjacent portions within each of the signals. As aresult, wavefronts 300 a, 300 b, 300 n for the signals 120 a, 120 b, 120n may become misaligned as illustrated.

As will be understood, the labeling of the wavefronts 300 a, 300 b, 300n in FIGS. 3A, 3B and 3C is arbitrary. Any position in space and/or timeof an optical signal may be identified as a wavefront for purposes ofdiscussing wavefront or phase alignment with respect to other space-timepositions. The phase relationship or coherency of a bundle of light raysat one position in space-time may change as the bundle of light rayspropagates and is influenced by the medium through which it travels.Also, alterations in phase relationship experienced by a particularbundle of light rays may not be the same as that experienced by anotherbundle of light rays that come before or after. Therefore, the alignmentor misalignment of arriving wavefronts may change significantly from onemoment to the next, as illustrated by the varying alignment shown foreach wavefront 300 a, 300 b, 300 n illustrated.

When information carried by the optical signals 120 a, 120 b, 120 n iscontained in the phase of the signals, a conventional optical receiverthat would focus and concentrate the optical signals 120 a, 120 b, 120 n(such as an optic lens system) would produce focused light that is notcoherent and no longer carries the phase information. To be able toretrieve the information, a conventional optical receiver typicallyrequires some form of wavefront correction to restore the phaserelationship across the wavefronts 300 a, 300 b, 300 n of the signals120 a, 120 b, 120 n. In contrast, the optical receiver 150 describedhere is not affected by these perturbations (delays on the order of lessthan a wavelength).

Even if a conventional receiver employs a wavefront correctionmechanism, it cannot retrieve the carried information if the threesignals 120 a, 120 b, 120 n are highly incoherent due to different timedelays incorporated into the signals 120 a, 120 b and 120 n by either ofthe phase or time delay circuits 114 a, 114 b, whichever method orstructure may implemented. This is also illustrated in FIGS. 3A, 3B and3C. For illustrative purposes only, in this explanation, assume thateach wavefront is shown corresponding to a phase change in the lightbeams (phase transition between symbols). The distance between each ofthe wavefronts 300 a can represent a symbol length (or modulation rate)within the signal 120 a. Similarly, the distances between each of thewavefronts 300 b and between each of the wavefronts 300 n can alsorepresent the symbol length within the signals 120 b and 120 n,respectively.

An example of time or delay shifts of the wavefronts 300 b and 300 nwith respect to the wavefronts 300 a are illustrated here. As will beappreciated, to obtain these shifts or delays, the delay element 140 amay cause a delay (Delay a) equal to zero (no delay is injected), thedelay element 140 b may cause a delay equal to an amount Delay b, andthe delay element 140 n may cause a delay equal to an amount Delay n. Inone specific example, the Delay b may equal about 10% of the symbollength, while Delay n may equal to about 20% of the symbol length, andDelay a is equal to zero. Such delays are typically on the order ofhundreds and possibly thousands of wavelengths of the lasers but are onthe order of 0% to around 30% of the symbol length. In other words,multiple intensity-modulated beams with optically-large phasedistortions (hundreds to thousands of wavelengths) that correspond toelectrically-small phase delays (such as 30% or less of symbol length)can be overlaid in a resonator-based receiver without significant lossand the transmitted information can be recovered.

In some embodiments, the predetermined delay amount is an amount lessthan about 30% of a symbol length of symbols transmitted within thesecond optical beam 120 b. In other embodiments, the predetermined delayamount is an amount between about 5% and 20% of the symbol length andgreater than 100 wavelengths of the wavelength of the second opticalbeam 120 b.

By deliberating shifting/delaying either one or more of the controlsignals 115 a-115 n with respect to each other (electric path delaying)and/or one or more of the modulated beams after output from themodulators (optical path delaying), the modulated output signals 120a-120 n are incoherent, which renders the signals virtually undetectableby conventional receivers (when operating in hard-to-intercept mode). Byrefraining from using any delays, the output signals 120 a-120 n will berelatively coherent (aside from wavefront variations resulting frompropagation through air, etc.) and may be detectable by a conventionalreceiver (when operating in conventional mode).

FIGS. 3A, 3B, and 3C illustrate examples of time delays in multipleoptical signals emitted from multiple lasers where the wavefrontscorrespond to changes in phase of the light from one symbol segment toanother symbol segment. This results in detectable transitions betweensymbols. Various changes may be made to FIGS. 3A, 3B, and 3C. Forexample, the wavefronts 300 a, 300 b, 300 n here are examples only, andthe actual wavefronts obtained during use can vary widely based on anumber of factors.

As will be appreciated, the optical transmitters 100 a, 100 b can beactively controlled to switch from one mode to the other mode asdesired. For example, the respective control circuit 210 a, 210 b mayinclude a controller or other logic circuitry for controlling activationof the modes (and the associated amount of each channel delay) based onuser input or programming.

Although some examples illustrated and described above are directed toinjecting fixed electrical or optical path delays, other embodiments mayutilize programmable or variable time delays, such as any other signal,pseudorandom modulation, or other signals/timing that provide varyingdelays over time and per signal. This may result in increasedincoherency and therefore increased difficulty in detecting themodulated optical signals 120 a-120 n on one hand, and may allow forincreasing coherency by proper adjustment of the encoded data signalsand delays on the other hand. In other words, the optical transmitters100 a, 100 b may be configurable to inject large phase/time delays inthe optical signals 120 a-120 n to achieve non-detectability while alsohaving the ability to configure the optical signals 120 a-120 n toappear conventional (no delays) and be detectable by a conventionalreceiver.

Now referring to FIGS. 4 and 5, there are illustrated a method (400) oftransmitting optical signals and a method (500) of receiving opticalsignals in accordance with this disclosure and teachings.

On the transmit end, data within an input signal (or data signal) 110 isgenerated or received (step 410). A delay and modulation circuit 125receives at least one optical beam. (step 420). The delay and modulationcircuit also receives the data signal 110 and generates at least twomodulated optical beams 120 a-120 n (using the at least one opticalbeam) each having the data encoded therein (step 430). As describedabove, any suitable type of phase modulation or encoding (includingphase modulation combined with amplitude or frequency modulation) may beutilized. One of the modulated optical beams is delayed with respectanother by a delay amount. In other words, the encoded data (e.g.,symbols) of one modulated optical beam is delayed in time or phase withrespect the same encoded data of the other modulated optical beam. Theamount(s) of delay(s) may be less than a length of the symbolstransmitted on the optical beams 120 a-120 n and, in some embodiments,is an amount less than about 30% of a symbol length (and in some casesbetween about 5% and 25% of the symbol length) and greater than 100wavelengths of the laser wavelength. The resulting modulated opticalbeams 120 a-120 n (with one or more delays) are emitted and directed toa target (step 450).

To create the delayed version, two identical encoding signals may begenerated, and the delay is injected into the electrical path of oneprior to input to the modulators. These original and delayed versionsare applied to control the modulator to generate undelayed and delayedmodulated optical beams 120 a-120 n. In another embodiment, the delaymay be injected in the optical path of one optical beam after theoptical beams have been modulated by the same encoding signal.

On the receive end, a resonator-based optical receiver 150 receives themodulated optical beams 120 a-120 n with at least one beam being adelayed or shifted version of another beam (step 510). As will beappreciated, the transmitter and method used to generate these receivedmodulated optical beams 120 a-120 may be irrelevant to the receive end,as long as one constitutes a delayed or shifted version of another asdescribed or contemplated herein. One or more resonators (e.g., etalons)convert or demodulate the received optical beams 120 a-120 n intointensity-modulated (IM) beam energy 165 a-165 n (step 520). The IM beamenergy 165 a-165 n is transmitted and focused via optics 170 on andreceived by one or more detectors 180, such as one or more photodiodesor array of photodiodes (step 530). The detector also converts thereceived optical energy into electrical signal(s) 185 (step 540). Sincemost, if not virtually all, of the optical energy from each of theoptical beams 120 a-120 n is received at the detector 180, the detector180 is configured to provide an additive function to add the convertedelectrical signal(s) together (or generates individual signals that canbe added together) to generate a signal indicative of the intensity ofthe received optical beams (step 550). The converted electrical signal185 can then be further processed to determine or otherwise recover thedata represented by the detected phase changes in the optical beams 120a-120 n (step 560).

In addition to the embodiments described above, the novel opticaltransmitter(s) disclosed can also be configured to transmit additionaldata by changing or modulating the time delay(s) of the symboltransitions (or parts thereof) within each optical beam or as betweenoptical beams. In other words, the time delays (or phase delays) betweenthe modulations (carrying the persistent data in the optical beams) canbe used to carry non-persistent data. The time delays used in theexamples herein are time delays between the phase modulation (PM)elements of the persistent modulation scheme in the optical beams. Inother embodiments, not shown, the time delays may be delays of onlyphase modulation, delays of only another component type of modulation(e.g., frequency, amplitude, intensity, wavelength, etc.), or delaysbetween one or more different components in two beams (e.g., delay phasemodulation by one amount in one beam and delay amplitude modulation byanother amount in another beam).

The time delay between amplitude/intensity modulation parts of thepersistent modulation may or may not be present. The delays may bemodulated by frequency or amplitude components.

Changes over time in the delay(s) of the symbol transitions (asdescribed above) in the optical beam(s) can be detected by the opticalreceiver. Such changes may include on-off keying (e.g., delay or nodelay) and/or shifts in the amount(s) of added delay(s), or othermodulation scheme(s). In one embodiment, this modulation may be detectedby an optical position sensitive detector (PSD) to recover the datarepresented by the changes/modulation of the delays. In other words,positional movement(s) of the aggregated optical beam (e.g. thecollective centroid of multiple beams) can be used to convey, representand transmit/receive data.

In accordance with one aspect, controlled changes (or variations) in thedelay(s) of multiple optical beams (within each beam or with respect toeach other) can be used to carry information. This information can beextracted using resonator/etalon and PSD in combination. Variable delaysbetween the phase modulation components in the persistent channel withinthe optical beams cause positional change(s) of the collective centroidof the optical beams at the receiver. Accordingly, these changes can bedetected and thus, enable additional data carrying capabilities outsideof the primary or persistent data channel. As will be appreciated,implementation of this feature provides a secondary (or non-persistent)data channel in addition to the primary (or persistent) data channel.These two channels can be modulated independently of each other.Variations or changes in the time delay (phase delay) between each ofthe individual optical beams is used to transmit or carry anon-persistent communication signal. In other embodiments, signalamplitude of the individual optical beams can be used to transmit orcarry a non-persistent communications signal, or some combination oftime delay and amplitude changes.

Now referring to FIGS. 6A and 6B, collectively illustrated is anotherexample laser-based communication system 10 a having a multi-source(multi-laser) transmitter 600 and a resonator-based receiver 650 inaccordance with this disclosure for implementing transmission andreception of a persistent communications signal and a non-persistentcommunications signal. As will be appreciated, a number of components inthe system 10 a are the same or similar to various components in thesystem 10 (shown in FIGS. 1, 2A and 2B). Only additional descriptionnecessary for an understanding of this embodiment is set forth below.

Similar to the optical transmitter 100 a, 100 b, the transmitter 600includes a plurality of optical sources 116 a-116 n each for generatingand emitting a respective light/optical beam or wave 117 a-117 n(optical signals). Any number of optical sources 116 a-116 n may beutilized, as desired, including an embodiment in which there is a lasersource that generates a single optical beam 117 that is split andapplied to each of the modulator(s) 118 a-118 n. Each optical source 116a-116 n emits the light beam 117 a-117 n that is modulated by amodulator 118 a-118 n to generate and output the modulated opticalsignal or beam 620 a-620 n. As will be appreciated, each modulator 118may be configured to modulate each respective light beam 117 in one ormore ways.

The optical transmitter 600 includes a delay and modulation circuit 125configured to include one (or both) of the phase or time delay circuits114 a, 114 b. The persistent data or input signal 110 is applied to theencoder 112 that generates one or more control signals 115 forcontrolling, at a minimum, phase modulation of the optical beam(s) bythe modulators 118 a-118 n. In this embodiment, the signal(s) 115 mayalso include multiple signals as described above with respect to thetransmitter 100 a.

When only the delay circuit 114 a is utilized, it receives controlsignal(s) 115 and generates multiple time-delayed (or offset) controlsignal(s) 615 a-615 n. As will be appreciated, the control signal(s)115/615 a-615 n are generated by the persistent channel encoder 112 andcarry the data of the persistent signal 110 (primary channel). Each ofthe time-delayed control signals 615 a-615 n is used to individuallymodulate its respective optical source 116 a-116 n and carry thepersistent data channel (primary channel) in each beam. The opticaltransmitter 600 includes a non-persistent channel encoder 612 a (orcontrol circuit) configured to receive an input/data signal 610 (i.e.,non-persistent data signal), such as a digital bit stream, and generateone or more control signal(s) 611 a. As will be appreciated, the encoder612 a receives input information and generates control signal(s)utilized to control the time delay(s) 140 a-140 n to additionallymodulate or change the time delay(s) in accordance with a desiredencoding protocol established for transmission of data within thenon-persistent signal 610. In other words, the control signal(s) 611 a(when applied to the phase or delay circuit 114 a) modulate or modifyproperties of the optical beam(s) in order to carry the information byvirtue of the changing/modulating delays. The data signal 610 includingthe data may be in analog or digital form.

The non-persistent channel encoder 612 a controls operation of the delayelements 140 a-140 n in order to control operation and/or length of eachdelay injected in the resulting control signals 615 a-615 n. The encoder612 a is shown in block diagram form. Persons of ordinary skill in theart will readily understand that any suitable device(s), logic, orcircuits (and methods) may be utilized, as desired, to generate andoutput delay control signals for controlling the delay elements 140a-140 n to provide delay(s) in the signal paths 615 a-615 n inaccordance with the teachings herein. As will be appreciated, theencoder 612 may be controlled by a processor (not shown) operating inaccordance with one or more software or firmware programs. The encoder612 may be further configured to operate the transmitter 600 in one ormore modes of operation, as described above with respect to thetransmitter(s) 100.

In essence, the transmitter 600 (when utilizing the delay circuit 114 a)operates in accordance with the operations of the transmitter 100 adescribed above by modulating the optical beams to carry the data signal110 (i.e., the persistent communications), but may also be configured tomodulate certain aspects of the optical beams to carry additional datafrom the signal 610 (i.e., the non-persistent communications). In theembodiment shown, the delay(s) of the control signals 615 a-615 n arecontrolled in a predetermined manner to represent or carry the datasignal 610. As a result, the modulated optical beams 620 a-620 n carryboth the persistent data and the non-persistent data.

When only the delay circuit 114 b is utilized, the modulators 118 a-118n each receive control signal(s) 115 for controlling, at a minimum,phase modulation of the optical beam(s) by the modulators 118 a-118 n—assimilarly described above with respect to optical transmitter 100 b—andgenerate modulated optical signals or beams. The optical transmitter 600includes a non-persistent channel encoder 612 b configured to receivethe input/data signal 610 (i.e., non-persistent data signal), such as adigital bit stream, and generate one or more control signal(s) 611 b. Aswill be appreciated, the encoder 612 b receives input information andgenerates control signal(s) utilized to control the time delay(s) 141a-141 n to additionally modulate or change the time delay(s) inaccordance with a desired encoding protocol established for transmissionof data within the non-persistent signal 610. In other words, thecontrol signal(s) 611 b (when applied to the phase or delay circuit 114b) modulate or modify properties of the modulated optical beams outputfrom the modulators 118 a-118 n in order to carry the information (i.e.,non-persistent data 610) by virtue of the changing/modulating the timedelays. Thus, it should be appreciated that the non-persistent data isencoded in the difference between the delays in some embodiments. Someof the delays may be constant, but the non-persistent informationcommunication techniques described herein work as long as at least oneof the time delays is variable. In some embodiments, having at least twovariable delays is helpful to make signal harder to intercept under someconditions. The data signal 610 including the data may be in analog ordigital form.

One or more of the modulated optical signals or beams coming from themodulators 118 a-118 n are input to the delay circuit 114 b. The phaseor time delay circuit 114 b functions to intentionally inject a time orphase delay into one or more of the modulated optical beams prior totransmission to a target. In this embodiment, for example, the circuit114 b includes the one or more delay elements 141 a-141 n, where eachdelay element functions to inject or generate a time delay of apredetermined specified amount (which can be fixed, programmable, orotherwise variable). The value(s) and/or variation(s) of the delay(s)are manipulated or programmed which results in the carrying ofinformation or data.

In essence, the transmitter 600 (when utilizing the delay circuit 114 b)operates in accordance with the operations of the transmitter 100 bdescribed above by modulating the optical beams to carry the data signal110 (i.e., the persistent communications), but also functions tomodulate certain aspects of the optical beams to carry additional datafrom the signal 610 (i.e., the non-persistent communications). In theembodiment shown, the delay(s) are controlled in a predetermined mannerto represent or carry the data signal 610. As a result, the modulatedoptical beams 620 a-620 n carry both the persistent data and thenon-persistent data.

As will be appreciated, although the transmitter 600 may be implementedin the manner described using the delay circuit 114 a or 114 b, somecombination of the two circuits may be utilized to inject the delay(s)as desired.

In another embodiment (not shown), the encoder 612 may optionallygenerate additional control signals for input directly to the modulators118 a-118 n and control or modulate one or more other characteristics(e.g., amplitude, intensity, frequency, wavelength, etc.) of the opticalbeams 117 a-117 n in accordance with the non-persistent data signal 610.In yet another embodiment, a combination of time/phase delay(s) andamplitude modulation may be implemented as the basis for carrying thenon-persistent data.

It will be understood that other methods, means or circuits forintentionally causing the time delay(s) between the optical signals orbeams 620 a-620 n may be utilized as determined by those of ordinaryskill in the art. For example, utilization of local clocking systemsassociated with each modulator/beam pair could also be controlled toimplement delays that result in the desired optical signals or beams 620a-620 n.

It will be appreciated that only those components of the opticaltransmitter 600 needed to explain and understand the concepts, methods,and systems disclosed herein are shown in FIG. 6A and described here.Although not shown, the optical transmitter 600 may include variousother components as needed or desired. Additional optics may also beincluded, such as one or more mirrors or lenses, which direct each ofthe modulated optical signals 620 a-620 n for output. For example, theoptics can be used to direct the modulated optical signals 620 a-620 nin a direction of the optical receiver 650 via a signal path as shown inFIGS. 6A and 6B.

In the illustrated embodiment in FIG. 6B, the optical receiver 650includes the resonator 160, one or more optics 170, and an opticalposition detector 680. As will be appreciated, the example opticalreceiver 650 is a resonator-based receiver as described above inconnection with the resonator 160 and optics 170 in the previousembodiments.

The variations in each of the received optical signals 620 a-620 n arerepresentative of the modulation performed at the optical transmitter600. That is, the variations may be representative of information (bothpersistent data and non-persistent data) encoded at the opticaltransmitter 600. The resonator 160 transforms the variations into anintensity modulation of output optical signal energy, which are shown asoutput optical signal energy 665 a-665 n in FIG. 6B. More specifically,the resonator 160 converts a phase modulation of each received opticalsignal 620 a-620 n in part by interaction of the arriving optical signal620 a-620 n with resonant optical signal energy accumulated within theresonator 160.

The output optical signal energy 665 a-665 n of each received opticalbeam is directed to the detector 680 via the optics 170. The detector680 converts the emerging intensity-modulated output optical signalenergy 665 a-665 n into one or more electrical signal(s) 685. Thedetector 680 functions to sum the intensity-modulated output opticalsignal energy 665 a-665 n and output an electrical signal(s)representing the total power received at the detector 680, which may befurther processed by a digital or analog processing subsystem to recoverthe persistent data payload—as described in previous embodiments.

In the illustrated embodiment, the detector 680 is an optical positionsensitive detector (PSD) 680. PSDs (also referred to asposition-sensitive diodes) are optical detectors known in the art, suchas PSDs manufactured by Hamamatsu or FirstSensor, and no furtherdescription of their general operation other than needed for anunderstanding of the present disclosure will be provided. The PSD 680 issensitive to (and can measure/detect) the position of a light beam/spoton the detector's surface. The PSD 680 illustrated in FIG. 6B is aquadrant position detector capable of measuring light in four quadrants,and may further enable summation and subtraction/differential functionson select quadrants—as shown. For example, to detect and recover thepersistent data carried in the multiple optical beams, the opticalsignal energy 665 a-665 n can be summed and processed. However, thebandwidth of typical PSDs are relatively low and may be utilized torecover the persistent data channel in implementations where thetransmission rate of the persistent channel falls within the bandwidthof the PSD (while also recovering the non-persistent data channel). Itmay be possible that other devices having the same or similarcapabilities as a typical PSD, but with higher bandwidth, could also beutilized for higher transmission rates of the persistent data channel.In other embodiments (not shown), the emerging intensity-modulatedoutput optical signal energy 665 a-665 n may be split and a portion ofthe signal energy directed to a PSD (for recovery of the non-persistentchannel) and another portion directed to another optical detector, suchas a conventional optical detector or the detector 180 of FIG. 1 (forrecovery of the persistent channel). In another embodiment, the receivedoptical beams could be split prior to input the resonator 160 and oneportion directed to the optical receiver 650 (having an resonator 160,optics 170 and PSD 680, FIG. 6B) and another portion directed to theoptical receiver 150 (having an resonator 160, optics 170 and detector180, FIG. 1) or a conventional optical receiver. These embodiments couldbe accomplished with a beam splitter or other structure or optics knownto those skilled in the art.

The encoder 612 a and the phase or time delay circuit 114 a functiontogether to introduce one more varying delays in the control signalscontrolling the modulators modulating the optical beams. Likewise, theencoder 612 b and the phase or time delay circuit 114 b functiontogether to introduce one more varying delays in the modulated opticalbeams that are output by the modulators. Adding these delay(s)effectively causes high frequency movement and a change in the positionof the collective/aggregate centroid of the combined laser beams asreceived by the PSD 680. By applying a given modulation scheme for thedelay(s), the resulting movement of the collective centroid of thereceived optical beams can be detected, and the data encoded accordingto the modulation of the delays at the transmitter 600 may be recovered.In other words, the actual location or change in location of thecollective (or aggregated) centroid of the received optical beams on thesurface of the PSD 680 can be used as a means or mechanism for thetransmission and detection of data, i.e., non-persistent data. Locationand/or positional changes of the combined centroid are controllable (anddetectable) by modulating/changing the phase/time delays between thetransmitted laser beams or within each beam individually.

As will be appreciated, both the inclusion of persistent data within themodulated laser beams 620 a-620 n and scintillation resulting from eachoptical path will cause slight movements in the centroid of eachreceived beam. However, the amount and direction of movement is mostlyrandom. In accordance with the present disclosure, it has beendetermined that changing or modulating phase/time delays of the symboltransitions of each optical beam with respect to each other at thetransmitter 600 can cause the combined centroid of the beams to move aswell. Detection of these movement(s) enables data to be decoded andreceived.

Now turning to FIG. 7, there is provided a diagram illustrating threeoutput intensity signals 665 a, 665 b, 665 n generated by the resonator160 in response to the receipt of three modulated optical beams 620 a,620 b, 620 n each having a different time delay for symbol transitions.The intensity output curves of each are related to each respectivetransmitted symbol. These variations are used by the receiver todetermine the transmitted symbol. On the right side of FIG. 7, there isshown the PSD 680 with an illustration of each intensity beam signalincident on the PSD 680. This illustrates the incidence of each beam 665a, 665 b, 665 n as if each were the only beam incident thereon(illustrating a centroid area containing most of the beam energy and anouter periphery area containing less beam energy).

At a given time t, the position of the collective centroid of the threebeams depends on the current location and magnitude of the threeindividual beam centroids. In the FIG. 7, the trajectory along which thecollective centroid typically moves (in one example) over time is shownby the oddly shaped curve 690 near the long time average combined beamcentroid on the PSD 680.

When the amount of delay between the symbol transitions in one opticalbeam and the same symbols in another optical beam is modulated orshifted (e.g., on-off delay keying), the centroid of the beam “wanders”or moves on the PSD 680; the frequency content of this motion iscontrolled by the frequency content of the modulation. The frequencycontent of the motion carries non-persistent information or data. Aswill be appreciated, this can be detected by the PSD 680. In otherembodiments, the length of each delay in multiple beams could bemodulated with respect to each other. For example, if the delays in twobeams are originally 10% and 25% of the symbol rate, respectively, theycould be changed to 0% and 15%, and back again at a given rate, etc.

In some embodiments, the modulation rate(s) of the phase/time delays(i.e., the frequency with which the time delays are changed) may be onthe order of 2 to 4 orders of magnitude less than the persistent datachannel symbol rate. For example, if the symbol rate is 100 Msymbols/second, the modulation rates for the non-persistent channelwould be on the order of 1 MHz down to 10 KHz.

In other embodiments, amplitudes of the laser beams may be modulated tocarry non-persistent data. To implement this, the encoder 612 outputsadditional control signal(s) (not shown) to the modulators 118 a-118 nto modulate the amplitude of the optical beams 117 a-117 n at the lowermodulation rate to carry the non-persistent data 110 (or portionthereof). Such amplitude modulation may be utilized alone or incombination with phase/delay modulation as described above.

Turning to FIG. 8, there is shown a different PSD 800 that may be usedfor the detection of rms (amplitude) of the centroid movement. While thePSD 680 is a four quadrant and two-dimensional PSD, the PSD 800 may besuitable for rms amplitude measurement and is shown including a firstelement (a circle) and a second element (a concentric outer ring)—asshown.

It will be understood that the present disclosure is not limited to anyspecific methods and modulation schemes. The present disclosure isbroadly directed to the modulation of the phase/time delay(s) of symboltransitions (carrying the persistent data in a primary channel) encodedon laser beams for non-persistent data communications (in a secondarychannel). This may include the modulation of different phase/timedelay(s) in different laser beams with respect to each other, or withineach beam itself. The present disclosure is broadly directed todetecting a change in location of the combined centroid of two or morereceived optical beams whereby the detected change represents datacarried therein.

Note that while communication in FIGS. 6A and 6B is shown as beingone-way from the optical transmitter 600 to the optical receiver 650,devices may include both an optical transmitter 600 and an opticalreceiver 650 (such as an optical transceiver) to support bidirectionaldata communication. Each transceiver may be capable of bidirectionaldata communication with another transmitter/receiver pair. In addition,FIGS. 6A and 6B illustrate one example of a laser-based communicationsystem 10 a having a multi-source (multi-laser) transmitter 600 and aresonator-based receiver 650, various changes may be made to the system.For example, the system 10 a may include any suitable number oftransmitters 600, receivers 650, and/or transceivers incorporatingtransmitters 600 and receivers 650.

Now referring to FIGS. 9 and 10, there are illustrated a method oftransmitting optical signals (900) and a method of receiving opticalsignals (1000) in accordance with this disclosure and teachingsassociated with the embodiments of FIGS. 6A, 6B, 7 and 8. On thetransmit end, a persistent input signal (or data signal) 110 is receivedand/or generated (step 910). An encoder 112 receives this data signaland generates persistent communication control signal(s) 115 inaccordance with the data signal 110 (step 920). As described above, anysuitable type of phase modulation or encoding (including phasemodulation combined with amplitude or frequency modulation) may beutilized. In addition to encoding the persistent data channel, anon-persistent input signal (or data signal) 610 is received and/orgenerated (step 915). One or more encoders 612 a, 612 b receive thissignal and generate one or more non-persistent communications controlsignal(s) 611 a, 611 b in accordance with the data signal 610 (step925).

In one embodiment, a phase or delay circuit 114 a receives and delaysthe control signal(s) 115 by one or more different amounts in accordancewith the control signal(s) 611 a to produce one or more second controlsignals 615 a-615 n (step 930) for controlling the modulators 118 a-118n. The control signal(s) 611 a in essence further modify or change thedelay elements 140 a-140 n over time in accordance with a modulation orencoding scheme—which result in varying time delays between the phasemodulations (persistent channel) in the respective output optical beams620 a-620 n. Thus, the non-persistent data is encoded by changing anamount of time delay between the optical beams 620 a-620 n output by thetransmitter.

The output beams 117 a-117 n emitted from the multiple optical sources116 a-116 n (such as multiple lasers) are modulated by the modulators118 a-118 n according to the one or more second control signal(s) 615a-615 n. This modulation results in the optical beams carrying thepersistent data (the data signal 110) and the non-persistent data (thedata signal 610). The amount(s) of delay(s) may be less than a length ofthe symbols transmitted on the optical beams 620 a-620 n and, in someembodiments, is an amount less than about 30% of a symbol length (and insome cases between about 5% and 25% of the symbol length) and greaterthan 100 wavelengths of the laser wavelength. Each of the multipleoptical sources 116 a-116 n (which may all have the same or similarwavelength) is modulated using the one or more second control signals615 a-615 n (step 940), and the resulting modulated optical beams 620a-620 n are emitted and directed to a target (step 950).

In another embodiment, the delay(s) may be injected into modulatedoptical beams (carrying the persistent data) output from the modulators118 a-118 n—i.e., after persistent data is modulated on the opticalbeams by the modulators. This may be implemented with the phase or delaycircuit 114 b receiving the control signal(s) 611 b and delaying themodulated optical beams after output from the modulators 118 a-118 n inaccordance with the control signal(s) 611 b to produce the beams 620a-620 b. The control signal(s) 611 b in essence further modify or changethe delay elements 141 a-141 n over time for varying the delay(s)between respective optical beams 620 a-620 n and, thus, carrying thenon-persistent data.

On the receive end, a resonator-based optical receiver 650 receivesmodulated optical beams 620 a-620 n that have been generated accordingto the optical transmitter 600—as described above. The optical receiver650 receives optical beams carrying persistent data (via persistent datachannel modulation applied to the modulators) and non-persistent data(via non-persistent data channel modulation applied to variations indelay(s) among the received beams) (step 1010). One or moreresonators/etalons 160 convert or demodulate the received optical beams620 a-620 n into intensity-modulated (IM) beam energy 665 a-665 n (step1020). The IM beam energy 665 a-665 n is transmitted and focused viaoptics 170 onto and received by one or more position sensitive detectors(PSD) 680 (step 1030). The detector 680 also converts the receivedoptical energy into one or more electrical signal(s) 685 (step 1040).

The PSD 680 is capable of providing the total energy of incoming beams620 a-620 n. As noted above, if the PDS 680 is capable of following thechanges of total energy at frequencies above those where the persistentdata is transmitted, the converted electrical signal output from the PSDcan be further processed to decode and recover the persistentinformation or data represented by the detected phase changes in theoptical beams 620 a-620 n (step 1060)—similar as that described abovewith respect to the operation of the optical receiver 150. However, ifthe PSD 680 bandwidth is too low, a separate conventional detector oranother resonator-based receiver (as described herein) may be employed.

In addition, the PSD 680 detects one or more changes in location orposition of the collective centroid or the received beams (step 1055).This detection can then be further processed to determine or otherwiserecover the non-persistent data represented by the detected changes inthe position of the centroid of the aggregated optical beams 620 a-620 n(step 1065). As described herein, the disclosure provides examples oftwo variables of the PSD output that can carry information: 1) frequencycontent of the centroid motion can be deterministically controlled bythe time delays and, thus, carry information and 2) rms (root meansquare) of the motion can also be deterministically controlled by thetime delays and, thus, carry information. The modulation scheme appliedto the time delays is conceptually the same a conventional AM and FMradio transmission where AM uses low frequency components of rms of thesignal to carry information, and FM uses changes in frequency content ofthe signal to carry information. Form this, signal processing andrecovery of the carried information is conventional. Determiningfrequency content and rms of a PSD output are typically known art (e.g.,Fourier transformation, perform a wavelet analysis, bypass filter; usingan AM-type receiver).

In some embodiments, various functions described in this patent documentare implemented or supported by a computer program that is formed fromcomputer readable program code and that is embodied in a computerreadable medium. The phrase “computer readable program code” includesany type of computer code, including source code, object code, andexecutable code. The phrase “computer readable medium” includes any typeof medium capable of being accessed by a computer, such as read onlymemory (ROM), random access memory (RAM), a hard disk drive (HDD), acompact disc (CD), a digital video disc (DVD), or any other type ofmemory. A “non-transitory” computer readable medium excludes wired,wireless, optical, or other communication links that transporttransitory electrical or other signals. A non-transitory computerreadable medium includes media where data can be permanently stored andmedia where data can be stored and later overwritten, such as arewritable optical disc or an erasable storage device.

It may be advantageous to set forth definitions of certain words andphrases used throughout this patent document. The terms “application”and “program” refer to one or more computer programs, softwarecomponents, sets of instructions, procedures, functions, objects,classes, instances, related data, or a portion thereof adapted forimplementation in a suitable computer code (including source code,object code, or executable code). The term “communicate,” as well asderivatives thereof, encompasses both direct and indirect communication.The terms “include” and “comprise,” as well as derivatives thereof, meaninclusion without limitation. The term “or” is inclusive, meaningand/or. The phrase “associated with,” as well as derivatives thereof,may mean to include, be included within, interconnect with, contain, becontained within, connect to or with, couple to or with, be communicablewith, cooperate with, interleave, juxtapose, be proximate to, be boundto or with, have, have a property of, have a relationship to or with, orthe like. The phrase “at least one of,” when used with a list of items,means that different combinations of one or more of the listed items maybe used, and only one item in the list may be needed. For example, “atleast one of: A, B, and C” includes any of the following combinations:A, B, C, A and B, A and C, B and C, and A and B and C.

The description in the present application should not be read asimplying that any particular element, step, or function is an essentialor critical element that must be included in the claim scope. The scopeof patented subject matter is defined only by the allowed claims.Moreover, none of the claims invokes 35 U.S.C. § 112(f) with respect toany of the appended claims or claim elements unless the exact words“means for” or “step for” are explicitly used in the particular claim,followed by a participle phrase identifying a function. Use of termssuch as (but not limited to) “mechanism,” “module,” “device,” “unit,”“component,” “element,” “member,” “apparatus,” “machine,” “system,”“processor,” or “controller” within a claim is understood and intendedto refer to structures known to those skilled in the relevant art, asfurther modified or enhanced by the features of the claims themselves,and is not intended to invoke 35 U.S.C. § 112(f).

While this disclosure has described certain embodiments and generallyassociated methods, alterations and permutations of these embodimentsand methods will be apparent to those skilled in the art. Accordingly,the above description of example embodiments does not define orconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

What is claimed is:
 1. An optical transmitter comprising: an opticallaser source configured to output at least one optical beam; and a delayand modulation circuit configured to: receive first data, receive seconddata, receive the at least one optical beam, transmit, using the atleast one optical beam, a first modulated optical beam encoded with thefirst data in accordance with a predetermined modulation scheme, andtransmit, using the at least one optical beam, a second modulatedoptical beam encoded with the first data in accordance with thepredetermined modulation scheme, wherein the second modulated opticalbeam is a time-delayed version of the first modulated optical beam, andwherein the delay and modulation circuit is configured to encode thesecond data by modulating time delays between the first and secondmodulated optical beams.
 2. The optical transmitter of claim 1, whereinthe predetermined modulation scheme comprises at least one of phase,amplitude, intensity, or frequency modulation.
 3. The opticaltransmitter of claim 1, wherein: the optical laser source comprises afirst laser source configured to output a first optical beam and asecond laser source configured to output a second optical beamsimultaneously with the first optical beam; and the delay and modulationcircuit comprises: a modulator configured to receive the first opticalbeam and the second optical beam and generate the first modulatedoptical beam and the second modulated optical beam, a delay elementconfigured to cause a delay in the second modulated optical beam, and anencoder configured to vary the delay in accordance with the second data.4. The optical transmitter of claim 3, wherein the delay element isdisposed within an optical path associated with the second modulatedoptical beam.
 5. The optical transmitter of claim 3, wherein the delayelement is disposed within an electrical signal path associated with thesecond modulated optical beam.
 6. The optical transmitter of claim 3,wherein the delay is an amount of time that is less than a timeassociated with a symbol length of symbols transmitted within the secondmodulated optical beam.
 7. The optical transmitter of claim 6, wherein amagnitude of the amount of time is between about 5% to about 30% of thetime associated with the symbol length.
 8. A method of transmittingoptical signals, the method comprising: receiving first data; receivingsecond data; receiving at least one optical beam; transmitting, usingthe at least one received optical beam, a first modulated optical beamencoded with the first data in accordance with a predeterminedmodulation scheme; and transmitting, using the at least one receivedoptical beam, a second modulated optical beam encoded with the firstdata in accordance with the predetermined modulation scheme, wherein thesecond modulated optical beam is a time-delayed version of the firstmodulated optical beam, and wherein the second data is encoded bymodulating time delays between the first and second modulated opticalbeams.
 9. The method of claim 8, wherein: receiving the at least oneoptical beam comprises: receiving a first optical beam from a firstlaser source, and receiving a second optical beam from a second lasersource simultaneously with receiving the first optical beam; and themethod further comprises: modulating the first optical beam to generatethe first modulated optical beam, modulating the second optical beam togenerate the second modulated optical beam, delaying, by a delay amount,the second modulated optical beam in relation to the first modulatedoptical beam, and encoding the second data by modulating the delayamount.
 10. The method of claim 9, wherein delaying, by the delayamount, the second modulated optical beam in relation to the firstmodulated optical beam comprises: generating a delay within an opticalpath associated with the second modulated optical beam.
 11. The methodof claim 9, wherein delaying, by the delay amount, the second modulatedoptical beam in relation to the first modulated optical beam comprises:generating a delay within an electrical signal path associated with thesecond modulated optical beam.
 12. The method of claim 8, wherein thepredetermined modulation scheme comprises at least one of phase,amplitude, intensity, or frequency modulation.
 13. An optical receivercomprising: an optical resonator configured to: receive a firstmodulated optical beam carrying first data and comprising apredetermined modulation, receive a second modulated optical beamcarrying the first data and comprising the predetermined modulation,wherein the received second modulated optical beam is a time-delayedversion of the received first modulated optical beam, convert thereceived first modulated optical beam into a first intensity-modulated(IM) beam, and convert the received second modulated optical beam into asecond IM beam; and a position sensitive detector configured to detectpositional changes of a combined centroid of the first IM beam and thesecond IM beam, the detected positional changes indicative of seconddata.
 14. The optical receiver of claim 13, wherein: the positionsensitive detector is further configured to: receive the first IM beamand the second IM beam, and generate and output an electrical signalhaving a magnitude indicative of an intensity of a sum of the first IMbeam and the second IM beam, and the optical receiver further comprisesa processor configured to process the detected positional changes torecover the second data.
 15. The optical receiver of claim 13, whereinthe predetermined modulation comprises at least one of phase, amplitude,intensity, or frequency modulation.
 16. A method of receiving opticalsignals, the method comprising: receiving, at a resonator-based opticalreceiver, a first modulated optical beam carrying first data andcomprising a predetermined modulation; receiving, at the resonator-basedoptical receiver, a second modulated optical beam carrying the firstdata and comprising the predetermined modulation, wherein the receivedsecond modulated optical beam is a time-delayed version of the receivedfirst modulated optical beam; converting the received first modulatedoptical beam into a first intensity-modulated (IM) beam; converting thereceived second modulated optical beam into a second IM beam; receiving,at a detector, the first IM beam and the second IM beam; and detectingpositional changes of a combined centroid of the first IM beam and thesecond IM beam at the detector, the detected positional changesindicative of second data.
 17. The method of claim 16, furthercomprising: generating an electrical signal having a magnitudeindicative of an intensity of a sum of the first IM beam and the secondIM beam; processing the electrical signal to recover the first data; andprocessing the detected positional changes to recover the second data.18. The method of claim 16, wherein the received second modulatedoptical beam is time-delayed by a delay amount that is less than about30% of a time associated with a symbol length of symbols within thereceived second modulated optical beam.
 19. The method of claim 16,further comprising: receiving, at the resonator-based optical receiver,a third modulated optical beam carrying the first data and comprisingphase modulations, wherein the received third modulated optical beam isanother time-delayed version of the received first modulated opticalbeam; converting the received third modulated optical beam into a thirdIM beam; receiving, at the detector, the third IM beam; and generatingand outputting an electrical signal having a magnitude indicative of anintensity of a sum of the first IM beam, the second IM beam, and thethird IM beam.
 20. The method of claim 16, wherein the predeterminedmodulation comprises at least one of phase, amplitude, intensity, orfrequency modulation.